I dunno, I can see both sides of what you guys are say, and I can see what the writers are saying...
When dealing with with firearms and the defense (dodging) test, you are not responding to the bullet, but to where the barrel is pointed at (bullets travel FAST, as in the hundreds to thousands of feet per second!)
It's not a case of "oh look! a bullet is coming at me, better side step!" but more of a case of "Crap, he's pointing a gun at me! move out of the way!!"
SO, a defender behind total cover is 100% protected... but he also can not see where that gun is pointed. (but the attacker as no idea where the defender is too!)
SO now we look at what is actually happening by rules. The attacker is -6 for blind fire, the defender is +4 defense, but unaware of the attack.
by Mechanics of SR, it would look like this: Attacker's gun pool: <Attribute>+<Skill>, +/- modifiers.
Defender's defense pool: <attribute>+<attribute>, +/- modifiers.
(or Full defense for <Attribute>+<attribute>+<attribute> +/- modifiers)
So Mechanically, when the defender runs into a room, and around the corner, breaking LOS, and the attacker choice to continue to attack it would look like this:
Attacker: rolls : <Attribute>+<attribute> -6 blind fire, +/- anything else.(range, smartlink, scope/site, environmental)
While the defender rolls <attribute>+Attribute> + <unaware> +4 full cover +/- anything else
So the attackers pool is at least -6 if not more.
while the defender is reduced to a pool of +4 (full cover) [the unaware removes the normal defense pool of the defender, leaving only the situational bonus]
All said, that means that the defender has a total defense of 10. (the -6 for the attacker, the +4 for total cover)
If attacker wins, follow the rules for shooting through a barrier to find the damage that must be resisted.. (if any)
if the defender wins. Stop. (but feel free the add a little colorful description as to hearing/seeing the rounds rip through the wall, or splatt against it... as appropriate)